CHAPTER XXV 



CLASS AVES. BIRDS. 



I. Sub-class. Arch^ORNITHES (or Saurura;) e.xtinct Archivopteryx. 

 II. Sub-class. Neornithes. 



1. Division, Ratitae. " Running Birds. " Ostrich, &c. 



2. Division, OdontolcK. Extinct toothed birds, Hes- 



perornis, &c. 



3. Division, Carinatoe. "Flying birds" with keeled 



sternum. 



Birds share with Mammals the rank of the highest Verte- 

 brates. Their muscles and skeleton, heart and lungs — 

 indeed, most of their structural arrangements — are not less 

 differentiated than those of Mammals. Nor are they in- 

 ferior in integration. The body temperature, exceeding 

 that of all other animals, is a physiological index to their 

 rapid metabolism, to their intense activity. Most Mammals 

 show a higher degree of brain development, and a closer 

 organic connection between mother and offspring, but the 

 truth is that the two classes represent markedly divergent 

 lines of progress. 



Life having begun in the waters, in all likelihood not far 

 from the sea-shore, slowly gained possession of the dry land 

 and then of the air. Insects among the lower animals, and 

 Birds among the higher, are pre-eminently the creatures of 

 the air ; intensely vivacious, typically beautiful in form and 

 colour, lovely and delightful in their ways. 



In the Birds we observe a marked increase of emotional 

 life, so that their affection for their mates, their care of their 

 young, the joyousness of their mood, often bursting forth in 

 song, have become proverbial among us. With their power 

 of flight they are emblems of freedom. 



